The physical properties of concretes, mortars and grouts have been improved by including organic fibers in the mixtures. A wide variety of organic polymer fibers have been introduced into concrete mixtures in the form of monofilaments, fibrillated sheet materials and fibrils. The optimal polymers are chemically inert and devoid of groups which undergo hydrolysis in the initial wet mixtures and final 'set' compositions. Polyolefin and steel fibers, in particular, have proven to have superior tensile strain capacity and stability and to improve the concretes and mortars to which they have been added.
The fibers become micromechanically bonded to the cementitious products during the hydration and polymerization reactions, in part from shrinkage of the cementitious components during the setting reactions. They can provide impact, shatter and abrasion resistance, plastic shrinkage crack control, improved post-cracking characteristics, and prolonged fatigue life. However, in order to provide these and other improved characteristics, it is essential that the fibers be uniformly dispersed in the initial mixtures.
Prior to this invention, fibers used in cementitious compositions were sold as bulk, packaged fibrillated or monofilament fibers, or fibrils. The fibers were typically added to the mixer with the cement, sand, aggregate, other admixtures, and water. The longer fibers tend to clump and ball, particular at higher concentrations, and the shearing action of the mixer and composition components was relied upon to separate and disperse the fibers. Because of the opacity and texture of the cementitious mixtures, no visual monitoring of the mixing is possible. Examination of set cementitious compositions, however, reveals that optimal unbundling and efficient uniform dispersion of the fibers is not usually achieved.